import tkinter,sys,time
root=tkinter.Tk()
root.minsize(500, 500)
Label1=tkinter.Label(text=time.strftime('%Y-%m-%d %H:%M:%S',time.localtime(time.time())))
Label1.pack()
def trickit():
    currentTime=time.strftime('%Y-%m-%d %H:%M:%S',time.localtime(time.time()))
    Label1.config(text=currentTime)
    root.update()
    Label1.after(1000, trickit)
Label1.after(1000, trickit)

root.mainloop()